There has long been a need for valves which could be interposed between two fluid-conducting members, typically between lengths of well pipe, and operated from a remote location to control fluid flow between the two fluid-conducting members. Considering downhole safety valves employed in oil and gas wells as one of the more exacting applications for such valves, it is to be noted that prior-art workers have for many years proposed and refined such valves and that the trade has come to prefer valves in which the movable valve member is held in one position by fluid supplied under pressure and usually actuated to its other position by a yieldable bias, typically applied by a compression spring. Though various types of movable valve members have been employed, rotatable elements in the form of a spherical ball are frequently preferred, and though a variety of pressure fluid operated actuating devices are used, actuators of the rack-and-pinion type have proved advantageous. The general state of the art for such valves is thus illustrated by the following United States patents:
______________________________________ 2,125,330 Brisbane 2,238,609 Sewell 2,708,563 Backman et al 2,786,535 Boer et al 3,035,808 Knox 3,104,862 Pearson 3,665,955 Conner 3,724,501 Scott ______________________________________
Though devices of this general type have been successful and have achieved considerable acceptance in the field, there has been an increasing need to decrease the size and increase the dependability of such valves without a corresponding increase in cost, and there has accordingly been a continuing need for improvement.